The crisis-hit Democratic Unionist Party has its third leader in just two months, after Jeffrey Donaldson was crowned without a contest.
The relative moderate replaces Edwin Poots – who was forced out after agreeing to a Sinn Fein demand in order to restore the new power-sharing executive at Stormont.
In an early warning shot, Mr Donaldson warned of the threat to “peace and stability” without changes to the Northern Ireland Protocol, which has imposed a post-Brexit trade border in the Irish Sea.
Unionists are fiercely opposed to the Protocol – and the weakening of ties with the rest of the United Kingdom it has brought – and have repeatedly called for it to be scrapped.
Mr Donaldson said he would be “speaking with the prime minister at the earliest opportunity” to make clear the level of Unionist opposition.
“The government and those who claim to be protectors of peace and stability, must step up and deal with the Protocol in a manner which respects the constitutional and economic integrity of the United Kingdom,” he said.
Brandon Lewis, the Northern Ireland Secretary, said he looked forward to working with Mr Donaldson and on “ensuring we deliver on the shared interests of all the people of Northern Ireland”.
However, he has vowed to use the UK Parliament to force through Irish language legislation – the Sinn Fein demand – if Stormont fails to act by September, setting the scene for a likely future clash.
Meanwhile, the outgoing Mr Poots raised eyebrows by claiming he has received a personal assurance from London that significant changes will be made to the Protocol.
Mr Donaldson is the province’s longest-serving MP, but is likely to quit his Lagan Valley seat after 24 years in order to become the new first minister at Stormont.
He was narrowly defeated by Mr Poots in the previous leadership contest, just three weeks ago, and was the only candidate when nominations closed this time.
In a statement, he pointed to the Northern Ireland Assembly as “the place where every element of our society is represented”, saying: “The coalition government is unwieldy, but it ensures every voice is heard.”
But he added: “I will play my part but the government and Brussels must step up and recognise the flaws of the Protocol and how it was foisted upon Northern Ireland.”
Boris Johnson has repeatedly threatened to suspend the Protocol unless the EU backs down on requiring the checks and restrictions he signed up to.
But he has been warned that Brussels has multiple weapons it can deploy that would have “significant economic consequences” for the UK, if the conflict escalates.
The EU is likely to shut off the flow of vital security and business data and could “slow down” exports through Calais, it was said.
Tensions have cooled a bit – with Brussels likely to agree a three-month delay to a ban on the sale of chilled meats across the Irish Sea – but that will only kick the can down the road.
